You can still use separate filing credentials when filing online.

You'll have two options when you file the return:

• Manually type in the credentials that you use to log into the HMRC website – this can be any user ID and password that's registered to file online for this Unique Taxpayer Reference.
• Click on Use my gateway credentials imported from the previous year’s tax return to auto-populate the relevant information – you can use this if you've imported a return from the previous year that has the specific credentials you want to file with again.